EXPONDIST in WPS Spreadsheet: Waiting-Time Probability or Density

=EXPONDIST(x,lambda,cumulative)

Supply all three arguments. x is the nonnegative time or value at which to evaluate the model. lambda is the positive rate. cumulative selects TRUE for the lower-tail cumulative probability and FALSE for probability density. The cited syntax does not provide an omitted-mode default, so use an explicit Boolean.

For x ≥ 0 and rate λ > 0, the independent model is CDF = 1 − exp(−λx) and density = λ exp(−λx). The mean waiting time is 1/λ. If your mean wait is five minutes, the rate is 0.2 per minute, not 5. Keep x and λ in compatible units.

Enter B2 = 3 for minutes waited and B3 = 0.2 for events per minute.

D2 is the probability of a wait of at most three minutes; D4 is the probability of waiting longer. D3 is density per minute, not a 10.98% probability of waiting exactly three minutes. In the continuous model, probability at one exact point is zero.

Put 2 in F2 and 5 in F3. Enter:

=EXPONDIST(F3,$B$3,TRUE)-EXPONDIST(F2,$B$3,TRUE)

Independent expected result: 0.302440604864197. The two cumulative values are approximately 0.632120558828558 and 0.329679953964361. Their difference is the probability of a wait between two and five minutes under this model. Subtracting density heights would not compute that area.

As a unit check, three minutes is 180 seconds and 0.2 per minute is 0.2/60 per second. =EXPONDIST(180,0.2/60,TRUE) has the same independent expectation as the first example. Density changes units: =EXPONDIST(180,0.2/60,FALSE) is approximately 0.00182937212031342 per second, one-sixtieth of the per-minute density.

Boundary controls are also informative: =EXPONDIST(0,0.2,TRUE) has mathematical expectation 0, while =EXPONDIST(0,0.2,FALSE) has expectation 0.2. Density need not be below one for every possible rate.

WPS documents #VALUE! when x or lambda is nonnumeric, and #NUM! when x is negative or lambda is nonpositive. The examples use numeric cells and literal TRUE/FALSE. Coercion of numeric-looking text, blanks and non-Boolean mode arguments has not been tested.

The exponential model assumes a constant event rate and has the memoryless property. A function returning a number does not establish that observed service times or arrivals follow this model. Check the model separately, especially when the process has a hard minimum time or a changing rate.

For very large λx, probabilities can round close to one and a complementary subtraction can lose small-tail detail. These moderate examples do not establish WPS extreme-tail precision. EXP explains the underlying exponential calculation, but evaluating a model independently is not a native test of EXPONDIST. No retirement or universal equivalence with another spelling is asserted.

The official WPS EXPONDIST lesson was published 2019-06-19 and labels its applicable edition WPS Office for Windows Personal. The lesson was checked on October 19, 2026. This establishes a documented-by date, not the release in which the function first appeared. No numeric build, last supported version or retirement date is established. Mac, Linux, web, mobile and global-English edition parity are unverified.

Original expected results here are independent calculations or explicitly labelled test expectations, not native WPS execution. No WPS screenshot or installed-build test is claimed. Formula separators and displayed decimal precision can depend on the target setup; verify the exact function name in that installation before distributing a workbook.